1. Field of the Invention
The present invention relates to a heat exchanger for use in an air conditioning unit of an automobile for cooling or warming a compartment of the automobile.
2. Description of the Related Art
A heat exchanger of the related art is disclosed in Japanese Patent Provisional Publication No. 10-170175. As shown in FIGS. 1 and 2, the heat exchanger 6 is comprised of a first intake port 9, a first outlet port 10, a sub-condenser 11, a second intake port 12, a second outlet port 13, a case 14, header pipes 15a, 15b, heat transfer tubes 16 and fins 17.
The first intake port 9 admits first coolant to flow into the heat exchanger 6 from a condenser. The first outlet port 10 admits first coolant to flow into an evaporator from the heat exchanger 6. First ends of the header pipes 15a, 15b are connected to the first intake port 9 and the first outlet port 10, respectively. The header pipes 15a, 15b extend along a longitudinal direction of the heat exchanger 6 in mutually spaced relationship. The plural heat transfer tubes 16 are connected to second ends of the header pipes 15a, 15b. The heat transfer tubes 16 extend along the longitudinal direction of the heat exchanger 16 in mutually spaced relationship. The plural fins 17 are disposed between the adjacent heat transfer tubes 16, 16. The sub-condenser 11 includes the header pipes 15a, 15b, the heat transfer tubes 16 and the fins 17. The second intake port 12 admits second coolant to flow into the heat exchanger 6 from the evaporator. Second coolant is created upon evaporation of first coolant. The second outlet port 13 admits second coolant to flow into a compressor from the heat exchanger 6. The case 14 is coupled to the second intake port 12 and the second outlet port 13 to seal peripheries of the sub-condenser 11 in airtight and liquid-tight relationship.
First coolant (as indicated by an arrow A in the figure) delivered from the first intake port 9 into the sub-condenser 11 undergoes heat-exchange with second coolant (as indicated by an arrow B in the figure) delivered from the second intake port 12 into the case 14. During such heat-exchange, first coolant is cooled with second coolant.
The heat exchanger of the related art has problems described below.
Due to the presence of second coolant flowing through the case 14 in direct contact with outer peripheries of the heat transfer tubes 16 through which first coolant flow, when using fluid, such as water, generating external corrosion as second coolant, the heat transfer tubes 16 suffer from corrosions caused by second coolant.
If corrosions occur on the heat transfer tubes 16, second coolant is mixed with first coolant in the case 14. Therefore, between first and second coolants, pressure of either one of coolants is imparted to the other coolant. This leads the heat exchanger 6 to be damaged.
Also, since the heat transfer tubes 16 are accommodated in the case 14, it is hard to find corroded states of the heat transfer tubes.